Hyperthyroidism in Cats: Symptoms, Diagnosis & Treatments

Hyperthyroidism is a common glandular disorder that can affect any breed of cat, male or female. It occurs when there is an excessive amount of thyroid hormone, particularly T4, in the bloodstream, leading to an increased metabolism. This condition mostly affects older cats, typically those over 10 years of age, with the average diagnosis age being between 12 and 13 years.

Symptoms You Need To Watch Out For

The earliest and most noticeable signs of hyperthyroidism in cats include sudden weight loss despite an increased appetite. About 98% of affected cats show weight loss while still eating more than usual. Other symptoms to be aware of include:

• Excessive drinking and thirst
• Increased urination
• Hyperactivity and restlessness
• An unkempt, messy coat appearance
• Panting or increased respiration rate
• Diarrhoea
• Increased shedding
• Heart disease signs, including rapid heart rate
• High blood pressure (hypertension)

Occasionally, vomiting may occur, but this is seen in around 50% of cats with this illness. These symptoms arise because the high levels of thyroid hormone affect multiple organs and systems in the body.

How Vets Diagnose Hyperthyroidism

Many health problems in senior cats share similar signs to hyperthyroidism, such as diabetes, intestinal diseases, inflammatory bowel disease, and chronic kidney disease. To make an accurate diagnosis, veterinarians conduct a combination of tests, including blood tests and urinalysis. A thyroid hormone blood test measuring T4 levels is the primary indicator of hyperthyroidism.

However, some cats may have normal thyroid hormone levels even when affected, possibly due to other illnesses suppressing T4 production. In these cases, vets may need to perform additional tests or use specialized thyroid testing to confirm the diagnosis.

Effective Treatments for Hyperthyroidism

Treatment options vary depending on the cat’s individual condition, age, and general health. The most common treatments include:

1. Medication

Oral medications that block thyroid hormone production can be effective within two to three weeks, with many cats responding well. Side effects may occur in about 20% of cases, including loss of appetite, vomiting, lethargy, bleeding problems, jaundice, itching around the head or face, and rarely, blood cell abnormalities. Most side effects are mild and often resolve without needing to discontinue treatment. Cats require lifelong medication and regular blood monitoring.

2. Surgery

Surgical removal of the affected thyroid gland can cure hyperthyroidism, particularly when caused by benign tumours called adenomas. However, surgery may not be suitable for many older cats due to risks related to anaesthesia and potential underlying heart or kidney conditions.

3. Radioactive Iodine Therapy

This treatment involves a single injection of radioactive iodine, which destroys the overactive thyroid tissue without the need for surgery or anaesthesia. Though very effective, cats must stay in a veterinary facility for 10 to 14 days for radioactive monitoring before returning home. This option is costly but offers a lasting cure for many cats.

What Causes Hyperthyroidism?

The exact causes remain uncertain but some factors thought to contribute include thyroid hormone imbalances linked to iodine levels in cat foods and environmental exposure to certain fire-retardant chemicals and soy-based ingredients common in cheaper commercial diets. Owners should carefully review cat food ingredients and consult their vets for nutritional guidance.

Conclusion

If your senior cat is losing weight despite a good appetite or shows any of the signs above, it is essential to see a vet promptly for testing. Early diagnosis and treatment can make a significant difference, helping your cat feel more comfortable and maintain a better quality of life.